Handbook of - ENPAB · Handbook of Biological Wastewater Treatment Design and Optimisation of Activated Sludge Systems Second Edition A.C. van Haandel and J.G.M. van der Lubbe

Handbook ofBiological Wastewater Treatment

Handbook ofBiological Wastewater TreatmentDesign and Optimisation of Activated Sludge Systems

Second Edition

A.C. van Haandel andJ.G.M. van der Lubbewww.wastewaterhandbook.com

Published by IWA Publishing

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London SW1H 0QS, UK

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First published 2012© 2012 IWA Publishing

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ISBN 9781780400006 (Hardback)ISBN 9781780400808 (eBook)

Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv

Notes on the second edition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii

About the authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxiii

Symbols, parameters and abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxv

Chapter 1Scope of text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Advances in secondary wastewater treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2 Tertiary wastewater treatment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.3 Temperature influence on activated sludge design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.4 Objective of the text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Chapter 2Organic material and bacterial metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.1 Measurement of organic material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.1.1 The COD test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.1.2 The BOD test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122.1.3 The TOC test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.2 Comparison of measurement parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.3 Metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.3.1 Oxidative metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182.3.2 Anoxic respiration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202.3.3 Anaerobic digestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Chapter 3Organic material removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253.1 Organic material and activated

sludge composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263.1.1 Organic material fractions

in wastewater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263.1.2 Activated sludge composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.1.2.1 Active sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293.1.2.2 Inactive sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293.1.2.3 Inorganic sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293.1.2.4 Definition of sludge fractions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3.1.3 Mass balance of the organic material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313.2 Model notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363.3 Steady-state model of the activated sludge system . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3.3.1 Model development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383.3.1.1 Definition of sludge age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.3.1.2 COD fraction discharged with the effluent . . . . . . . . . . . . . . . . . . . . . . 403.3.1.3 COD fraction in the excess sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403.3.1.4 COD fraction oxidised for respiration . . . . . . . . . . . . . . . . . . . . . . . . . . 443.3.1.5 Model summary and evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

3.3.2 Model calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493.3.3 Model applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

3.3.3.1 Sludge mass and composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533.3.3.2 Biological reactor volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563.3.3.3 Excess sludge production and nutrient demand. . . . . . . . . . . . . . . . . . 583.3.3.4 Temperature effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623.3.3.5 True yield versus apparent yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633.3.3.6 F/M ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

3.3.4 Selection and control of the sludge age. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 673.4 General model of the activated sludge system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

3.4.1 Model development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733.4.2 Model calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763.4.3 Application of the general model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

3.5 Configurations of the activated sludge system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 783.5.1 Conventional activated sludge systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 783.5.2 Sequential batch systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793.5.3 Carrousels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 813.5.4 Aerated lagoons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

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Chapter 4Aeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854.1 Aeration theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

4.1.1 Factors affecting kla and DOs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894.1.2 Effect of local pressure on DOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894.1.3 Effect of temperature on kla and DOs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914.1.4 Oxygen transfer efficiency for surface aerators . . . . . . . . . . . . . . . . . . . . . . . . . 924.1.5 Power requirement for diffused aeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

4.2 Methods to determine the oxygen transfer efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . 974.2.1 Determination of the standard oxygen transfer efficiency . . . . . . . . . . . . . . . . . 974.2.2 Determination of the actual oxygen transfer efficiency . . . . . . . . . . . . . . . . . . . 99

Chapter 5Nitrogen removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1075.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1075.1 Fundamentals of nitrogen removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

5.1.1 Forms and reactions of nitrogenous matter . . . . . . . . . . . . . . . . . . . . . . . . . . . 1085.1.2 Mass balance of nitrogenous matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105.1.3 Stoichiometrics of reactions with nitrogenous matter . . . . . . . . . . . . . . . . . . . . 115

5.1.3.1 Oxygen consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1155.1.3.2 Effects on alkalinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1175.1.3.3 Effects on pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

5.2 Nitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235.2.1 Nitrification kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1245.2.2 Nitrification in systems with non aerated zones. . . . . . . . . . . . . . . . . . . . . . . . 1345.2.3 Nitrification potential and nitrification capacity . . . . . . . . . . . . . . . . . . . . . . . . . 1365.2.4 Design procedure for nitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

5.3 Denitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1415.3.1 System configurations for denitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

5.3.1.1 Denitrification with an external carbon source . . . . . . . . . . . . . . . . . . 1425.3.1.2 Denitrification with an internal carbon source . . . . . . . . . . . . . . . . . . . 143

5.3.2 Denitrification kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1465.3.2.1 Sludge production in anoxic/aerobic systems . . . . . . . . . . . . . . . . . . 1465.3.2.2 Denitrification rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1475.3.2.3 Minimum anoxic mass fraction in the pre-D reactor . . . . . . . . . . . . . . 149

5.3.3 Denitrification capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1515.3.3.1 Denitrification capacity in a pre-D reactor . . . . . . . . . . . . . . . . . . . . . . 1515.3.3.2 Denitrification capacity in a post-D reactor . . . . . . . . . . . . . . . . . . . . . 153

5.3.4 Available nitrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1565.4 Designing and optimising nitrogen removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

5.4.1 Calculation of nitrogen removal capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1605.4.2 Optimised design of nitrogen removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

5.4.2.1 Complete nitrogen removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1665.4.2.2 Incomplete nitrogen removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

Contents vii

5.4.2.3 Effect of recirculation of oxygen on denitrification capacity . . . . . . . . 1725.4.2.4 Design procedure for optimized nitrogen removal . . . . . . . . . . . . . . . 177

Chapter 6Innovative systems for nitrogen removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1816.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1816.1 Nitrogen removal over nitrite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

6.1.1 Basic principles of nitritation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1846.1.2 Kinetics of high rate ammonium oxidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1876.1.3 Reactor configuration and operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1886.1.4 Required model enhancements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

6.2 Anaerobic ammonium oxidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1906.2.1 Anammox process characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1916.2.2 Reactor design and configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

6.3 Combination of nitritation with anammox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1956.3.1 Two stage configuration (nitritation reactor–Anammox). . . . . . . . . . . . . . . . . . 1956.3.2 Case study: full scale SHARON - Anammox treatment. . . . . . . . . . . . . . . . . . 1986.3.3 Single reactor configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

6.4 Bioaugmentation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2036.5 Side stream nitrogen removal: evaluation and potential . . . . . . . . . . . . . . . . . . . . . . . . 204

Chapter 7Phosphorus removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2077.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2077.1 Biological Phosphorus Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

7.1.1 Mechanisms involved in biological phosphorus removal . . . . . . . . . . . . . . . . . 2087.1.2 Bio-P removal system configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2127.1.3 Model of biological phosphorus removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214

7.1.3.1 Enhanced cultures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2147.1.3.2 Mixed cultures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2207.1.3.3 Denitrification of bio-P organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2257.1.3.4 Discharge of organic phosphorus with the effluent. . . . . . . . . . . . . . . 228

7.2 Optimisation of biological nutrient removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2297.2.1 Influence of wastewater characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2297.2.2 Improving substrate availability for nutrient removal . . . . . . . . . . . . . . . . . . . . 2317.2.3 Optimisation of operational conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2337.2.4 Resolving operational problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

7.3 Chemical phosphorus removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2397.3.1 Stoichiometrics of chemical phosphorus removal . . . . . . . . . . . . . . . . . . . . . . 239

7.3.1.1 Addition of metal salts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2397.3.1.2 Addition of lime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2417.3.1.3 Effects on pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242

7.3.2 Chemical phosphorus removal configurations. . . . . . . . . . . . . . . . . . . . . . . . . 2437.3.2.1 Pre-precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2457.3.2.2 Simultaneous precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247

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7.3.2.3 Post-precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2527.3.2.4 Sidestream precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253

7.3.3 Design procedure for chemical phosphorus removal . . . . . . . . . . . . . . . . . . . 255

Chapter 8Sludge settling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2598.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2598.1 Methods to determine sludge settleability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260

8.1.1 Zone settling rate test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2608.1.2 Alternative parameters for sludge settleability . . . . . . . . . . . . . . . . . . . . . . . . . 2638.1.3 Relationships between different settleability parameters. . . . . . . . . . . . . . . . . 264

8.2 Model for settling in a continuous settler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2668.2.1 Determination of the limiting concentration Xl . . . . . . . . . . . . . . . . . . . . . . . . . 2708.2.2 Determination of the critical concentration Xc . . . . . . . . . . . . . . . . . . . . . . . . . 2708.2.3 Determination of the minimum concentration Xm. . . . . . . . . . . . . . . . . . . . . . . 271

8.3 Design of final settlers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2748.3.1 Optimised design procedure for final settlers . . . . . . . . . . . . . . . . . . . . . . . . . 2748.3.2 Determination of the critical recirculation rate . . . . . . . . . . . . . . . . . . . . . . . . . 2788.3.3 Graphical optimization of final settler operation . . . . . . . . . . . . . . . . . . . . . . . . 2818.3.4 Optimisation of the system of biological reactor and final settler. . . . . . . . . . . 2838.3.5 Validation of the optimised settler design procedure . . . . . . . . . . . . . . . . . . . . 286

8.3.5.1 US EPA design guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2868.3.5.2 WRC and modified WRC design guidelines . . . . . . . . . . . . . . . . . . . . 2868.3.5.3 STORA/STOWA design guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . 2878.3.5.4 ATV design guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2878.3.5.5 Solids flux compared with other design methods . . . . . . . . . . . . . . . . 288

8.4 Physical design aspects for final settlers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2918.5 Final settlers under variable loading conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293

Chapter 9Sludge bulking and scum formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2979.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2979.1 Microbial aspects of sludge bulking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2979.2 Causes and control of sludge bulking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301

9.2.1 Sludge bulking due to a low reactor substrate concentration . . . . . . . . . . . . . 3019.2.2 Guidelines for selector design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3039.2.3 Control of bulking sludge in anoxic-aerobic systems. . . . . . . . . . . . . . . . . . . . 3059.2.4 Other causes of sludge bulking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

9.3 Non-specific measures to control sludge bulking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3109.4 Causes and control of scum formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

Chapter 10Membrane bioreactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31910.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31910.1 Membrane bioreactors (MBR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

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10.2 MBR configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32210.2.1 Submerged MBR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32410.2.2 Cross-flow MBR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32510.2.3 Comparison of submerged and cross-flow MBR . . . . . . . . . . . . . . . . . . . . . . 331

10.3 MBR design considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33510.3.1 Theoretical concepts in membrane filtration . . . . . . . . . . . . . . . . . . . . . . . . . 33510.3.2 Impact on activated sludge system design . . . . . . . . . . . . . . . . . . . . . . . . . . 33810.3.3 Pre-treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34410.3.4 Module configuration – submerged MBR. . . . . . . . . . . . . . . . . . . . . . . . . . . . 34510.3.5 Module aeration – submerged MBR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34610.3.6 Key design data of different membrane types . . . . . . . . . . . . . . . . . . . . . . . . 347

10.4 MBR operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34710.4.1 Operation of submerged membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34710.4.2 Operation of cross-flow membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34810.4.3 Membrane fouling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34810.4.4 Membrane cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349

10.5 MBR technology: evaluation and potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352

Chapter 11Moving bed biofilm reactors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35511.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35511.1 MBBR technology and reactor configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

11.1.1 Carriers used in MBBR processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35911.1.2 Aeration system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36011.1.3 Sieves and mixers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361

11.2 Features of MBBR process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36211.3 MBBR process configurations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364

11.3.1 Pure MBBR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36411.3.2 MBBR as pre-treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36511.3.3 MBBR as post-treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36611.3.4 Integrated fixed film reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367

11.4 Pure MBBR design and performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36711.4.1 Secondary treatment of municipal sewage . . . . . . . . . . . . . . . . . . . . . . . . . . 36711.4.2 Secondary treatment of industrial wastewater . . . . . . . . . . . . . . . . . . . . . . . . 37111.4.3 Nitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37211.4.4 Nitrogen removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37411.4.5 Phosphorus removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377

11.5 Upgrading of existing activated sludge plants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37811.5.1 High rate pre-treatment MBBR for BOD/COD removal . . . . . . . . . . . . . . . . . 37811.5.2 Upgrading of secondary CAS to nitrification . . . . . . . . . . . . . . . . . . . . . . . . . 37911.5.3 Nitrification in IFAS processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38111.5.4 IFAS for nitrogen removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384

11.6 Solids removal from MBBR effluent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38411.6.1 Gravity settling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384

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11.6.2 Micro-sand ballasted lamella sedimentation . . . . . . . . . . . . . . . . . . . . . . . . . 38511.6.3 Dissolved air flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38611.6.4 Micro screening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38611.6.5 Media filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39011.6.6 Membrane filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390

Chapter 12Sludge treatment and disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39112.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39112.1 Excess sludge quality and quantity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39212.2 Sludge thickeners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395

12.2.1 Design of sludge thickeners using the solids flux theory . . . . . . . . . . . . . . . . 39512.2.2 Design of sludge thickeners using empirical relationships . . . . . . . . . . . . . . 399

12.3 Aerobic digestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40312.3.1 Kinetic model for aerobic sludge digestion . . . . . . . . . . . . . . . . . . . . . . . . . . 403

12.3.1.1 Variation of the volatile sludge concentration . . . . . . . . . . . . . . . . 40412.3.1.2 Variation of the oxygen uptake rate . . . . . . . . . . . . . . . . . . . . . . . 40512.3.1.3 Variation of the nitrate concentration . . . . . . . . . . . . . . . . . . . . . . 40612.3.1.4 Variation of the alkalinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40612.3.1.5 Variation of the BOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409

12.3.2 Aerobic digestion in the main activated sludge process . . . . . . . . . . . . . . . . 41012.3.3 Aerobic digester design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41312.3.4 Optimisation of aerobic sludge digestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41912.3.5 Operational parameters of the aerobic digester . . . . . . . . . . . . . . . . . . . . . . 423

12.4 Anaerobic digestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43012.4.1 Stoichiometry of anaerobic digestion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43212.4.2 Configurations used for anaerobic digestion . . . . . . . . . . . . . . . . . . . . . . . . . 43512.4.3 Influence of operational parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43812.4.4 Performance of the high rate anaerobic digester. . . . . . . . . . . . . . . . . . . . . . 442

12.4.4.1 Removal efficiency of volatile suspended solids . . . . . . . . . . . . . 44212.4.4.2 Biogas production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44312.4.4.3 Energy generation in anaerobic sludge digesters. . . . . . . . . . . . . 44412.4.4.4 Solids destruction and stabilised excess

sludge production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44512.4.4.5 Nutrient balance in the anaerobic digester . . . . . . . . . . . . . . . . . . 446

12.4.5 Design and optimisation of anaerobic digesters . . . . . . . . . . . . . . . . . . . . . . 45112.5 Stabilised sludge drying and disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454

12.5.1 Natural sludge drying. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45512.5.2 Design and optimisation of natural sludge drying beds . . . . . . . . . . . . . . . . . 459

12.5.2.1 Determination of the percolation time (t2) . . . . . . . . . . . . . . . . . . . 45912.5.2.2 Determination of the evaporation time (t4) . . . . . . . . . . . . . . . . . . 46012.5.2.3 Influence of rain on sludge drying bed productivity. . . . . . . . . . . . 468

12.5.3 Accelerated sludge drying with external energy . . . . . . . . . . . . . . . . . . . . . . 46912.5.3.1 Use of solar energy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47012.5.3.2 Use of combustion heat from biogas . . . . . . . . . . . . . . . . . . . . . . 473

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Chapter 13Anaerobic pretreatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47713.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47713.1 Anaerobic treatment of municipal sewage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478

13.1.1 Configurations for anaerobic sewage treatment . . . . . . . . . . . . . . . . . . . . . . 48013.1.1.1 Anaerobic filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48013.1.1.2 Fluidised and expanded bed systems . . . . . . . . . . . . . . . . . . . . . 48113.1.1.3 Upflow anaerobic sludge blanket (UASB) reactor . . . . . . . . . . . . 48213.1.1.4 The RALF system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484

13.1.2 Evaluation of different anaerobic configurations . . . . . . . . . . . . . . . . . . . . . . 48413.2 Factors affecting municipal UASB performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486

13.2.1 Design and engineering issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48713.2.2 Operational- and maintenance issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49513.2.3 Inappropriate expectations of UASB performance . . . . . . . . . . . . . . . . . . . . 49613.2.4 Presence of sulphate in municipal sewage . . . . . . . . . . . . . . . . . . . . . . . . . . 49713.2.5 Energy production and greenhouse gas emissions. . . . . . . . . . . . . . . . . . . . 501

13.2.5.1 Carbon footprint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50113.2.5.2 Biogas utilization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506

13.3 Design model for anaerobic sewage treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51613.3.1 Sludge age as the key design parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . 51613.3.2 Influence of the temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52113.3.3 Characterisation of anaerobic biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522

13.4 UASB reactor design guidelines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52813.5 Post-treatment of anaerobic effluent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538

13.5.1 Secondary treatment of anaerobic effluent . . . . . . . . . . . . . . . . . . . . . . . . . . 53913.5.1.1 Applicability of the ideal steady state model for COD removal . . . 54213.5.1.2 Stabilisation of aerobic excess sludge in the UASB reactor. . . . . 553

13.5.2 Nitrogen removal from anaerobic effluent . . . . . . . . . . . . . . . . . . . . . . . . . . . 55913.5.2.1 Bypass of raw sewage to the activated sludge system . . . . . . . . 56013.5.2.2 Anaerobic digestion with reduced methanogenic efficiency . . . . . 56213.5.2.3 Application of innovative nitrogen removal configurations . . . . . . 564

13.5.3 Future developments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56613.5.3.1 Two stage anaerobic digestion . . . . . . . . . . . . . . . . . . . . . . . . . . . 56613.5.3.2 Psychrophilic anaerobic wastewater treatment . . . . . . . . . . . . . . 567

13.6 Anaerobic treatment of industrial wastewater. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568

Chapter 14Integrated cost-based design and operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 57514.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57514.1 Preparations for system design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 576

14.1.1 The basis of design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57714.1.1.1 Wastewater characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57714.1.1.2 Kinetic parameters and settleability of the sludge . . . . . . . . . . . . 582

14.1.2 Costing data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58214.1.2.1 Investment costs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583

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14.1.2.2 Operational costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58614.1.2.3 Annualised investment costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588

14.1.3 Performance objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58914.1.4 Applicable system configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59114.1.5 Limitations and constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592

14.2 Optimised design procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59514.2.1 System A1: Conventional secondary treatment. . . . . . . . . . . . . . . . . . . . . . . 59514.2.2 System A2: Secondary treatment with primary settling . . . . . . . . . . . . . . . . . 60714.2.3 System B1: Combined anaerobic-aerobic treatment . . . . . . . . . . . . . . . . . . . 61014.2.4 System C1: Nitrogen removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62114.2.5 System C2: Nitrogen and phosphorus removal . . . . . . . . . . . . . . . . . . . . . . . 62714.2.6 System comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633

14.3 Factors influencing design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63514.3.1 Influence of the wastewater temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . 63514.3.2 Influence of the sludge age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 636

14.4 Operational optimisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63814.4.1 Comparison of different operational regimes . . . . . . . . . . . . . . . . . . . . . . . . . 63814.4.2 Optimised operation of existing treatment plants. . . . . . . . . . . . . . . . . . . . . . 642

14.5 Integrated design examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64414.5.1 Nutrient removal in different configurations . . . . . . . . . . . . . . . . . . . . . . . . . . 64414.5.2 Membrane bioreactor design – case study . . . . . . . . . . . . . . . . . . . . . . . . . . 657

14.6 Final Remarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668

Reference list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671

Appendix 1Determination of the oxygen uptake rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685A1.1 Determination of the apparent OUR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 686A1.2 Correction factors of the apparent OUR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687

A1.2.1 Representativeness of mixed liquoroperational conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687

A1.2.2 Critical dissolved oxygen concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687A1.2.3 Hydraulic effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 688A1.2.4 Absorption of atmospheric oxygen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689A1.2.5 The relaxation effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692

Appendix 2Calibration of the general model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 695A2.1 Calibration with cyclic loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696A2.2 Calibration with batch loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 700

Appendix 3The non-ideal activated sludge system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703

Appendix 4Determination of nitrification kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709

Contents xiii

Appendix 5Determination of denitrification kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 717

Appendix 6Extensions to the ideal model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 723A6.1 Imperfect solid-liquid separation in final settler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 723

A6.1.1 Particulate organic nitrogen and phosphorus in the effluent . . . . . . . . . . . . 724A6.1.2 Excess sludge production and composition . . . . . . . . . . . . . . . . . . . . . . . . . 726

A6.2 Nitrifier fraction in the volatile sludge mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 727

Appendix 7Empiric methods for final settler sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 731A7.1 Stora design guidelines (1981). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 731

A7.1.1 Theoretical aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 731A7.1.2 Application of the STORA 1981 design guidelines . . . . . . . . . . . . . . . . . . . 734A7.1.3 Modifications to the STORA 1981 design guidelines . . . . . . . . . . . . . . . . . . 736

A7.2 Final settler design comparison methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 738A7.3 ATV design guidelines (1976) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 741

A7.3.1 Theoretical aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 741A7.3.2 Modifications to the ATV 1976 design guidelines. . . . . . . . . . . . . . . . . . . . . 744

Appendix 8Denitrification in the final settler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747

Appendix 9Aerobic granulated sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 754A9.1 Benefits of aerobic granular sludge systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 757A9.2 System design and operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 761

A9.2.1 Process configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 761A9.2.2 Reactor configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764A9.2.3 Operation of AGS systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764A9.2.4 Start-up of aerobic granular sludge reactors . . . . . . . . . . . . . . . . . . . . . . . . 767

A9.3 Granular biomass: evaluation and potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 767

Handbook of Biological Wastewater Treatmentxiv

Preface

In this book the authors seek to present the state-of-the-art theory concerning the various aspects of theactivated sludge system and to develop procedures for optimized cost based design- and operation. Thebook has been written for students at MSc or PhD level, as well as for engineers in consulting firms andenvironmental protection agencies.

Since its conception almost a century ago, the activated sludge system evolved as the most popularconfiguration for wastewater treatment. Originally this was due to its high efficiency at removingsuspended solids and organic material, which at that time was considered as the most importanttreatment objective.

The earliest design principles for activated sludge systems date back to the second half of the 20thcentury, almost fifty years after the first systems were constructed and many further developments haveoccurred since. As nitrogen is one of the key components in eutrophication of surface water, in the1970s nitrogen removal became a requirement and this resulted in the incorporation of nitrification- anddenitrification processes in the activated sludge system. An important subsequent development was theintroduction of chemical- and biological phosphorus removal in the 1980s and 1990s.

Over the last decades the predominance of the activated sludge system has been consolidated,as cost-efficient and reliable biological removal of suspended solids, organic material and themacro-nutrients nitrogen and phosphorus has consistently been demonstrated. This versatility is alsoshown in the continuous development of new configurations and treatment concepts, such asanaerobic pre-treatment, membrane bioreactors, granular aerobic sludge and innovative systems fornitrogen removal. It is therefore scarcely surprising that many books have been dedicated to thesubject of wastewater treatment and more specifically to one or more aspects of the activated sludgesystem. So why should you consider buying this particular book? The two main reasons why thisbook is an invaluable resource for everybody working in the field of wastewater treatment are thefollowing:

– The scope of this book is extremely broad and deep, as not only the design of the activated sludgesystem, but also that of auxiliary units such as primary and final settlers, pre-treatment units, sludgethickeners and digesters is extensively discussed;

– The book offers a truly integrated design method, which can be easily implemented in spreadsheets andthus may be adapted to the particular needs of the user.

In this text, the theory related to the different processes taking place in activated sludge systems is presented.It is demonstrated that the sludge age is the main design parameter for both aerobic and anaerobic systems. Asteady-state model is developed that will prove extremely useful for the design and optimisation of activatedsludge systems. This model describes the removal of organic material in the activated sludge system and itsconsequences for the principal parameters determining process performance: effluent quality, excess sludgeproduction and oxygen consumption.

The design guidelines for biological and chemical nutrient removal are integrated with those of othermain treatment units, such as final settlers, primary settlers and anaerobic pre-treatment units, sludgethickeners and -digesters. Finally, the text will also deal with operational issues: for example sludgesettling and -bulking, oxygen transfer, maintenance of an adequate pH, sludge digestion and methaneproduction.

Visit us at our website www.wastewaterhandbook.com for more information, the latest updates and freeExcel design tools, or contact us at [email protected].

Handbook of Biological Wastewater Treatmentxvi

Notes on the second edition

This significantly revised and updated second edition expands upon our earlier work. Valuable feedbackwas received from the wastewater treatment courses, based on this handbook, given in the period 2007to 2011. This welcome feedback has been incorporated in the book in order to improve the didacticqualities. Where needed the book structure was adapted to make it more intuitively understandable bythe reader, while many additional examples have been introduced to clarify the text. Finally, obsoletetext has been removed and a number of obvious errors corrected. The main additions/changes withregards to the book contents are:

Chapter 3 – Organic material removal

First of all, a new section has been written that explains the model notation used in this book in much moredetail. Additional examples facilitate the readers understanding about the way the steady state model forCOD removal is constructed and how it can be used. The difference between true and apparent yield isexplained, while also the section on the F/M ratio, and especially the reasons not to use it, has beenexpanded.

Chapter 4 – Aeration

The section on aeration, previously part of Chapter 3, has been updated and moved to a separate Chapter.

Chapter 5 – Nitrogen removal

The effect of the oxygen recycle to the anoxic zones on the denitrification capacity is now explicitly includedin the model. Furthermore, the concept of available nitrate, i.e. the flux of nitrate to the pre-D and post-Dzones is explained in more detail. The design procedure for nitrification has been elaborated and severalextensive examples for optimized design of nitrogen removal have been added.

Chapter 6 – Innovative systems for nitrogen removal

As the developments on the subject of innovative nitrogen removal are so rapid, this section has beensignificantly rewritten and expanded and now merits it own chapter.

Chapter 7 – Phosphorus removal

Several examples on the design of chemical phosphorus removal systems have been added.

Chapter 8 – Sludge settling

To explain the theory better, several examples have been added. The section on sludge thickening wasexpanded with an alternative empirical design approach and has been moved to Chapter 12 – SludgeTreatment and Disposal.

Chapter 9 – Sludge bulking and scum formation

The section on sludge separation problems has been rewritten and expanded to include the latest theories andexperimental findings on the development and prevention of both sludge bulking- and scum formation.

Chapter 10 – Membrane bioreactors

The chapter on new system configurations is now devoted toMBR only, as the section on aerobic granulatedsludge has been updated based on the return of experience from full-scale installations and is moved toAppendix A9. Several new examples detail the design of both cross-flow and submerged membraneconfigurations.

Chapter 11 – Moving bed biofilm reactors

A new chapter about a technology that has become popular due to its compactness and its potential forupgrading of existing activated sludge systems.

Chapter 12 – Sludge treatment and disposal

The chapter is expanded with a section on sludge thickening: both the solids flux design method and anempirical design approach are presented.

Chapter 13 – Anaerobic pre-treatment

This part has been completely rewritten based on the experiences obtained from an extensive review of largefull-scale UASB based sewage treatment plants. The main design and operational issues in UASB treatmentare discussed, while new sections have been introduced on the subject of the loss of methane with theeffluent, the impact on greenhouse gas emissions and the problems related to the presence of sulphate inthe raw sewage.

The anaerobic design model has been expanded to include the presence of sulphate in the influent and thatof suspended solids in the effluent. A new section has been introduced that deals with the methodology ofUASB reactor design. The section on combined anaerobic-aerobic treatment has been adapted to reflect thelatest findings on the extent of nitrogen removal possible after anaerobic pre-treatment. Some interestingnew treatment configurations are presented, combining anaerobic pre-treatment with innovative nitrogen

Handbook of Biological Wastewater Treatmentxviii

removal. Finally a thoroughly updated section on industrial anaerobic reactors has been included, based onthe authors experiences within Biothane Systems International.

Chapter 14 – Integrated cost-based design and operation

The section on cost calculation now contains several examples of the calculation of investment-, operationaland annualized costs. Furthermore the chapter is expanded with two extensive integrated design examples:(I) combined nitrogen and phosphorus removal in which bio-P removal is compared with pre- andsimultaneous precipitation and (II) MBR in which the system configurations for submerged andcross-flow membranes are evaluated.

List of model parameters

Complementary to the section on model notation, a comprehensive list of all parameters used throughout thebook has been compiled and added for easy reference.

New appendices

– Appendix A5 - determination of denitrification kinetics– Appendix A7 - empiric methods for final settler sizing– Appendix A8 - denitrification in the final settler– Appendix A9 - aerobic granulated sludge

Notes on the second edition xix

About the authors

Adrianus van Haandel (1948) holds an MSc degree from the Technical University of Eindhoven – TheNetherlands and a PhD from the University of Cape Town – South Africa. He has worked at theUniversity of Campina Grande in Brazil since 1971, where he coordinates research on biologicalwastewater treatment. He has extensive experience as an independent consultant and is involved with anumber of international expert committees. Together with other authors he has written several booksabout different aspects of wastewater treatment including “Anaerobic sewage treatment in regions with ahot climate” and “Advanced biological treatment processes for industrial wastewaters: principles andapplications”. Adrianus can be contacted at [email protected].

Jeroen van der Lubbe (1971) is a senior process & product development engineer at Biothane SystemsInternational, part of Veolia Water – Solutions and Technologies. Apart from process design andconsultancy, he has been responsible for the development of the UpthaneTM – Veolia’s municipal UASBsolution while currently he is product development manager of the anaerobic MBR – MemthaneTM andinvolved in the first European implementation. He graduated in 1995 at the Environmental Departmentof the Wageningen University – The Netherlands and since then has been involved extensively in thedesign, engineering and operation of both industrial and municipal wastewater treatment plants. Beforejoining Biothane, he worked at Fontes & Haandel Engenharia Ambiental, Raytheon Engineers &Constructors, DHV Water and Tebodin Consultants and Engineers. Jeroen can be contacted [email protected].

Acknowledgements

This book reflects the experience of the authors with different aspect of biological wastewater treatment.Insofar as the theory of biological processes is concerned, it has very much been influenced by the ideasdeveloped by the research group lead by Professor Gerrit Marais at the University of Cape Town –

South Africa. Another important input was the ongoing cooperative research program at severalBrazilian universities, PROSAB, financed by the federal government through its agency FINEP. Theexperimental results generated by this group and the discussions, especially with Professors Pedro Alemand Marcos von Sperling, constituted important contributions.

In the Netherlands, the following persons are acknowledged for their input: Merle de Kreuk at theTechnical University Delft and Tom Peeters from DHV BV – for their input to and review of the sectionon aerobic granular sludge, Wouter van der Star at the Technical University Delft and Tim Hülsen ofPaques BV – for their review of the section on innovative nitrogen removal, Darren Lawrence at KochMembrane Systems and Hans Ramaekers at Triqua BV – for their contribution to the section on MBRtechnology, Hallvard Ødegaard, professor emeritus at the Department of Hydraulic and EnvironmentalEngineering of the Norwegian University of Science and Technology in Trondheim, for his extensiveinput to the chapter on MBBR, Sybren Gerbens at the Friesland Water Authority – for his input onconstruction and treatment costs while he also provided several photos used in this book, André vanBentem at DHV BV and Joost de Haan at the Delfland Water Board who supplied many interestingphotos and finally Barry Heffernan for licensing photos and proofreading.

Finally a special word of thanks to the author’s wives, Paula Frassinetti and Lotje van de Poll, for theirunfailing support during the long incubation period in which this book….and the second edition was written.Not to mention the time it took to develop the course material…

Symbols, parameters and abbreviations

In this book a naming convention is used in which (I) the number of characters required to identify a uniqueparameter is minimized and (II) the description of the parameter can be deducted in a logical way from itsindividual constituents. Thus in general a parameter is constructed from a combination of one or more mainidentifiers (either in capital- or in normal font) followed by one or more subscripts (capital- or normal font).

The main identifiers indicate the class of the parameter, such as daily applied load or production (M),substrate (S), solids (X) or constants (K), while the subscripts specify the type involved, such as (v)=volatile, (t)=total, et cetera. Thus for example MSti is defined as the total (t) daily applied mass (M) oforganic material (S) in the influent (i). In most cases a specific letter can therefore have more than onemeaning. However, it should be easy to deduct what it refers to from the context where it is used. Assuch the amount of characters required to uniquely identify a specific parameter is reduced to the minimum.

In the remainder of this section the list of abbreviations and the list of symbols and parameters arepresented. The latter contains in alphabetical order all of the parameters used in the second edition of theHandbook, including a short description and the unit of measure. Subsequently, after a number of keyparameters have been introduced in the main text, the model notation used in this book will be explainedin much more detail in Section 3.2.

LIST OF ABBREVIATIONS

AF = anaerobic filterAIC = annualized investment costsAnammox = anaerobic (anoxic) ammonium oxidationAPT = activated primary tankAT = aeration tankATU = allyl-thio-ureaATV = abwasser technik verbandAF = anaerobic filterBABE = bio-augmentation batch enhanced

BAS = biofilm activated sludge systemBDP = BardenphoBOD = biological oxygen demandCANON = completely autotrophic nitrogen removal over nitriteCAS = conventional activated sludge systemCF = cross-flowCHP = combined heat and powerCIP = cleaning in placeCOD = chemical oxygen demandCSTR = completely stirred tank reactor (completely mixed reactor)DEMON = de-ammonificationDSVI = diluted sludge volume indexDWF = dry weather flowEGSB = expanded granular sludge bedEPA = environmental protection agencyFSS = fixed suspended solidsGLS = gas-liquid-solidsGSBR = granulated sludge bed reactorHUSB = hydrolysis upflow sludge blanketIC = internal circulationIFAS = integrated fixed film activated sludge systemISS = inert suspended solidsLPCF = low pressure cross-flowMBR = membrane bioreactorMBBR = moving bed biofilm reactorMF = micro-filtrationOGF = oil, grease and fatOLAND = oxygen limited autrotrophic nitrification – denitrificationOUR = oxygen uptake ratePAO = phosphate accumulating organismsPE = people equivalentPF = plug flowPHB = poly-hydroxy-butyratesRWF = rainy weather flow rateSBR = sequencing batch reactorSHARON = single reactor for high activity ammonium removal over nitriteSSVI3.5 = stirred sludge volume index (determined at 3.5 g · l−1)STORA = stichting toegepast onderzoek naar de reiniging van afvalwaterSTOWA = stichting toegepast onderzoek waterbeheerSVI = sludge volume indexTAC = total annualised costsTIC = total investment costsTKN = total Kjeldahl nitrogenTMP = trans-membrane pressureTOC = total operational costs

Handbook of Biological Wastewater Treatmentxxvi

TOC = total organic carbonTS = total solidsTSS = total suspended solidsUASB = upflow anaerobic sludge blanketUCT = university of Cape TownUF = ultra-filtrationVFA = volatile fatty acidsVS = volatile solidsVSS = volatile suspended solidsWRC = water research councilZSV = zone settling velocity

LIST OF SYMBOLS AND PARAMETERS

Par. Short description UoM

a = projected width of a gas collection plate m

a =mixed liquor recirculation factor(from nitrification zone to pre-D zone)

(–)

Aa = total area occupied by apertures in a UASB reactor m2

Ad = surface area of final settler m2

Admin =minimum final settler surface area m2

ai,n = annualisation factor (–)

AIC = annualized investment costs US$ · yr−1

Alk = alkalinity mg CaCO3 · l−1

Alk∞ = final alkalinity after complete decay of active sludge inaerobic digester

mg CaCO3 · l−1

Alkd = alkalinity consumed in the aerobic digester mg CaCO3 · l−1

Alki = initial alkalinity concentration (aerobic digestion) mg CaCO3 · l−1

Alke = final alkalinity concentration (aerobic digestion) mg CaCO3 · l−1

Am =membrane surface area m2

Amod =membrane surface area in a module m2

Ao = overflow area in UASB reactor m2

ath = specific thickener surface area m2 · d · kg−1 COD

Ath = thickener surface area m2

Au = surface area of UASB reactor m2

Aumin =minimum UASB surface area m2

b = projected height of a gas collection plate m

ban = anaerobic decay rate d−1

bh = decay rate for heterotrophic bacteria (non bio-P) d−1

bhT = decay rate for heterotrophic bacteria (non bio-P) attemperature T

d−1

Symbols, parameters and abbreviations xxvii

Bn =mass balance recovery factor for nitrogenous material (–)

bn = decay rate for nitrifiers d−1

Bo =mass balance recovery factor for COD (–)

BODvss = BOD value of a unit of organic sludge (aerobic digestion) mg BOD · mg−1 VSS

Bp =mass balance recovery factor for phosphorus (–)

bp = decay rate of bio-P organisms d−1

bv = apparent decay constant of heterotrophic bacteria (non bio-P) d−1

Cae = unit construction costs of aeration system US$ · kW−1

Cd = unit volume construction costs of final settler US$ · m−3

Cd1 = unit volume construction costs of the primary settler US$ · m−3

Cda = unit volume construction costs of aerobic digester US$ · m−3

Cdi = unit volume construction costs of anaerobic digester US$ · m−3

Cdl = costs of discharge to sewer (levies) US$ · PE−1

Cel = price of electricity US$ · kWh−1

Cgen = unit construction cost of power generation US$ · kW−1

Ch = costs of heating (e.g. with gas or oil) US$ · m−3 or kg−1 fuel

[CH4]eq = equilibrium methane concentration mg CH4 · l−1

cp = proportionality constant between stirred and dilutedsludge volume index

(–)

Cr = unit volume construction costs of the aeration tank US$ · m−3

Cr = specific active biomass production per unit mass daily appliedbiodegradable COD

mg VSS · d · mg−1 COD

Crh = specific active biomass production of heterotrophic organismsper unit mass daily applied biodegradable COD


Crn = specific active nitrifiers production of per unit mass of dailyapplied nitrifiable nitrogen

mg VSS · d · mg−1 N

Crp = specific active biomass production of bio-P organismsper unit mass daily applied biodegradable COD


Csd = costs of sludge disposal US$ · ton−1 TSS

Cth = unit volume construction costs of a sludge thickener US$ · m−3

Cu = unit volume construction costs of a UASB reactor US$ · m−3

Dc = denitrification capacity mg N · l−1 influent

Dc1 = denitrification capacity in pre-D zone mg N · l−1 influent

Dc1p = denitrification capacity from utilization of slowlybiodegradable COD

mg N · l−1 influent

Dc1s = denitrification capacity from utilization of easilybiodegradable COD


Dc3 = denitrification capacity in post-D zone mg N · l−1 influent

Dcd = denitrification capacity in the final settler mg N · l−1 influent

Dd = diameter of final settler m

Handbook of Biological Wastewater Treatmentxxviii

DOav = average oxygen concentration during OUR test mg O2 · l−1

DOl = oxygen concentration in the liquid phase mg O2 · l−1

DOm = oxygen concentration measured by oxygen sensor mg O2 · l−1

DOmt = oxygen concentration in the membrane tank mg O2 · l−1

DOs = saturation concentration of dissolved oxygenin the mixed liquor at pressure “p”

mg O2 · l−1

DOs20 = saturation concentration of dissolved oxygen at 20°C mg O2 · l−1

DOsa = saturation concentration of dissolved oxygenunder actual conditions

mg O2 · l−1

DOsp = saturation concentration of dissolved oxygen at standardpressure

mg O2 · l−1

DOss = saturation concentration of dissolved oxygenat 20°C and 1 atm (9.1 mg · l−1)

mg O2 · l−1

DOsT = saturation concentration of dissolved oxygenat temperature T

mg O2 · l−1

f = fraction of the influent flow discharged to thefirst reactor in step feed systems

(–)

f = endogenous residue mg VSS · mg−1 VSS

F = fouling factor (–)

F = solids flux kg TSS · m−2 · d−1

F/P = feed to permeate ratio (–)

fa(N-1) = active sludge fraction in the sludge entering the Nth digester mg VSS · mg−1 VSS

fac = fraction of construction costs required for constructionof additional (non-specified) units

mg VSS · mg−1 VSS

fae = active sludge concentration in aerobic digester mg VSS · mg−1 VSS

faer = aerobic sludge mass fraction kg TSS · kg−1 TSS

fai = initial active sludge concentration (aerobic digestion) mg VSS · mg−1 VSS

faN = active sludge fraction in the sludge leaving the Nth aerobicdigester

mg VSS · mg−1 VSS

fan = anaerobic sludge mass fraction kg TSS · kg−1 TSS

fat = active fraction of sludge mg VSS · mg−1 TSS

fav = active fraction of organic sludge mg VSS · mg−1 VSS

fav1 = active fraction of organic sludge from primary settling mg VSS · mg−1 VSS

fav2 = active fraction of organic sludge from activated sludge system mg VSS · mg−1 VSS

fave = active fraction of organic stabilised sludge mg VSS · mg−1 VSS

favu = active fraction of organic UASB sludge mg VSS · mg−1 VSS

fbh = fraction of Sbi consumed by normal heterotrophic biomass mg COD · mg−1 COD

fbp = fraction of Sbi sequestered by bio-P organisms mg COD · mg−1 COD

fbp = slowly biodegradable (particulate) COD fractionin the raw wastewater

mg COD · mg−1 COD

Symbols, parameters and abbreviations xxix

f′bp = slowly biodegradable (particulate) COD fractionin the pre-settled wastewater


fbpu = biodegradable particulate fraction of organic CODin anaerobic effluent


fbs = easily biodegradable (soluble) COD fraction in the rawwastewater


f′bs = easily biodegradable (soluble) COD fraction in the pre-settledwastewater


fbsh = fraction of Sbsi consumed by normal heterotrophic bacteria mg COD · mg−1 COD

fbsp = fraction of Sbsi sequestered by bio-P organisms mg COD · mg−1 COD

fbsu = biodegradable soluble fraction of organic COD in anaerobiceffluent


fcv = proportionality constant between bacterial mass and mass ofCOD

mg COD · mg−1 VSS

fd = activity factor for a bivalent ion (–)

fdn = denitrification constant= (1 - fcv·Y)/2.86 (–)

fep = endogenous residue of bio-P organisms mg VSS · mg−1 VSS

fh2s = inorganic H2S-COD in UASB effluent expressed as fractionof influent COD


fh2su = inorganic H2S-COD fraction in anaerobic effluent mg COD · mg−1 COD

fi = additional investment costs (non-construction related) (–)

Fl = limiting solids flux kg TSS · m−2 · d−1

Fm =membrane flux l · m−2 · h−1

fm =maximum anoxic sludge fraction allowed forselected sludge age (when Nae=Nad)

m3 · m−3

fm = activity coefficient for a monovalent ion in the mixed liquor (–)

fmax =maximum allowed anoxic mass fraction kg TSS · kg−1 TSS

fmi =mineral fraction influent mg ISS · mg−1 COD

fmin =minimum required anoxic sludge mass fraction kg TSS · kg−1 TSS

fn = nitrogen fraction in organic biomass mg N · mg−1 VSS

f′np = inert particulate COD fraction after primary settling mg COD · mg−1 COD

fnp = inert particulate influent COD fraction mg COD · mg−1 COD

fnpu = inert particulate fraction of COD in anaerobic effluent mg COD · mg−1 COD

f′ns = inert soluble COD fraction after primary settling mg COD · mg−1 COD

fns = non biodegradable, soluble influent COD fraction mg COD · mg−1 COD

fnsu = non biodegradable, soluble COD fraction in anaerobic effluent mg COD · mg−1 COD

fp = phosphorus fraction in organic biomass mg P · mg−1 VSS

fpd = fraction of bio-P organisms capable of denitrification (–)

fpp =maximum poly-P fraction of bio-P organisms mg P · mg−1 VSS

fpr = phosphorus release constant mg P · mg−1 COD

Handbook of Biological Wastewater Treatmentxxx

fpu = putrescible fraction of anaerobic sludge mg VSS · mg−1 VSS

fr = average frequency of exposure at the chlorine injection point d−1

Fs = applied solids load (drying beds) kg TSS · m−2

f′sb = fraction of biodegradable COD that is easily biodegradableremaining after primary settling

mg COD · mg−1 BCOD

fsb = fraction of biodegradable COD that is easily biodegradable mg COD · mg−1 BCOD

Fsol = solids loading rate kg TSS · m2 · d−1

Ft = total solids flux in final settler kg TSS · m2 · d−1

Fu = solids flux due to sludge abstraction kg TSS · m2 · d−1

fv = organic sludge fraction= ratio between volatile andtotal sludge concentration

mg VSS · mg−1 TSS

Fv = solids flux due to sludge settling kg TSS · m2 · d−1

fve = organic sludge fraction in stabilised sludge mg VSS · mg−1 TSS

fvp = organic sludge fraction of bio-P organisms mg VSS · mg−1 TSS

fvu = organic sludge fraction anaerobic sludge mg VSS · mg−1 TSS

fx = total anoxic sludge mass fraction kg TSS · kg−1 TSS

fx1 = pre-D anoxic sludge mass fraction kg TSS · kg−1 TSS

fx3 = post-D anoxic sludge mass fraction kg TSS · kg−1 TSS

fxd = sludge mass fraction located in final settler kg TSS · kg−1 TSS

fxvd = fraction of final settler volume filled with sludge m3 · m−3

g = gravitational acceleration constant m · s−2

h = liquid height above base of V-notch or above perforation m

H1 = thickener inlet zone / thickening zone (ATV) m

H2 = thickener clarification zone / sludge storage zone (ATV) m

H3 = thickener compression zone / separation zone (ATV) m

H4 = thickener sludge removal zone / clear water zone (ATV) m

Hd = height of final settler m

Hdav = average depth of final settler m

Hdb = height of the sludge buffer zone m

Hdf = deflector height m

Hdif = level of air diffusers above reactor bottom m

Hdig = height of digestion zone in UASB reactor m

Hfb = height of freeboard of UASB reactor m

Hgb = liquid height of gas box m

Hgls = liquid GLS height m

Hliq = liquid height UASB reactor m

Hth = height of sludge thickener m

Hu = total height of UASB reactor m

i = interest rate %

Symbols, parameters and abbreviations xxxi

I = investment costs US$

Idsv = diluted sludge volume index ml · g−1 TSS

Issv = stirred sludge volume index ml · g−1 TSS

k =Vesilind constant l · g−1 TSS

K1 = rate constant for denitrification on easilybiodegradable organic material

mg N · g−1 Xa-VSS · d−1

k1 = equilibrium constant for CO2 dissociation mol · l−1

k1* = “real” equilibrium constant for CO2 dissociation,corrected for ionic activity

mol · l−1

K2 = rate constant for denitrification on slowlybiodegradable organic material

mg N · g−1 Xa-VSS · d−1

k2 = equilibrium constant for bicarbonate dissociation mol · l−1

k2* = “real” equilibrium constant of the bicarbonate dissociation,corrected for ionic activity

mol · l−1

K3 = rate constant for denitrification due to endogenous respiration mg N · g−1 Xa-VSS · d−1

Ka = adsorption rate constant litre · mg−1 Xa · d−1

kabs = adsorption constant h−1

Kap = adsorption saturation constant mg COD · mg−1 Xa

Kc = fermentation constant l · mg−1 Xa-VSS · d−1

Kh =Henry constant atm or mg · l−1 · atm−1

kla = oxygen transfer coefficient h−1

klaa = oxygen transfer coefficient under actual conditions h−1

klas = oxygen transfer constant at 20°C h−1

klaT = oxygen transfer constant at T°C h−1

Km = specific utilisation rate constant mg COD ·mg−1 Xa · d−1

Kmp = specific utilisation rate of slowly bio-degradable (adsorbed)organic material

mg COD · mg−1 Xa · d−1

Kms = specific utilisation rate of easily biodegradableorganic material

mg COD · mg−1 Xa · d−1

Kn = saturation constant for nitrifiers mg N · l−1

Ko = half saturation constant for aerobic processes mg O2 · l−1

kr = relaxation constant h−1

Ks = saturation constant (Monod) mg COD · l−1

Ksp = saturation constant (Monod) for growth on slowlybiodegradable, adsorbed substrate

mg COD · mg−1 Xa

Kss = saturation constant (Monod) for growth on easilybiodegradable substrate

mg COD · l−1

kw = equilibrium constant for the dissociation of water mol2 · l−2

kw* = “real” equilibrium constant for the dissociation of water,corrected for ionic activity

mol2 · l−2

Handbook of Biological Wastewater Treatmentxxxii

Le = height of water layer remaining at end of drying period mm

Li = height of initial water layer applied to sludge bed mm

Lu = length of UASB reactor m

m =maintenance costs % of TIC per year

mciv =maintenance costs for civil part of plant % of TIC per year

MCrd = construction costs of aeration tank and final settler US$

MCthdi = total construction costs of thickener and anaerobic digester US$

MDc1 = total pre-D denitrification capacity kg N · d−1

MDc3 = total post-D denitrification capacity kg N · d−1

MEchem = total chemical excess sludge production kg TSS · d−1

mEd = specific digested sludge mass kg VSS · kg−1 COD

MEd = digested sludge mass kg VSS · d−1

MEmeoh = chemical excess sludge production (metal oxides) kg TSS · d−1

MEmep = chemical excess sludge production (metal phosphates) kg TSS · d−1

mEt = specific excess sludge production(equal to apparent yield Yap)

mg TSS · mg−1 COD

MEt = excess sludge production kg TSS · d−1

mEt1 = specific primary excess sludge production mg TSS · mg−1 COD

MEt1 = primary excess sludge production kg TSS · d−1

mEt2 = specific secondary excess sludge production mg TSS · mg−1 COD

MEt2 = secondary excess sludge production kg TSS · d−1

mEte = specific stabilised excess sludge production mg TSS · mg−1 COD

MEte = stabilised excess sludge production kg TSS · d−1

mEtu = specific anaerobic excess sludge production mg TSS · mg−1 COD

MEtu = anaerobic excess sludge production kg TSS · d−1

MEtx = total (secondary) excess sludge production corrected for lossof suspended solids in the effluent

kg TSS · d−1

mEv = specific organic sludge production (apparent yield Yap) mg VSS · mg−1 COD

MEv = volatile or organic excess sludge production kg VSS · d−1

MEv1 = organic primary excess sludge production kg VSS · d−1

MEv2 = organic secondary excess sludge production kg VSS · d−1

mEve = specific stabilised organic excess sludge production mg VSS · mg−1 COD

MEve = stabilised organic excess sludge production kg VSS · d−1

MEvu = organic anaerobic excess sludge production kg VSS · d−1

mEvxa = specific active excess sludge production mg VSS · mg−1 COD

mExvna = specific inactive excess sludge production mg VSS · mg−1 COD

mMd = specific methane production kg CH4 · kg−1 COD

MMd =methane production kg CH4 · d−1

MME = consumption of metal salts kg · d−1

Symbols, parameters and abbreviations xxxiii

mme&i =maintenance costs for mechanical, electrical andinstrumentation part of plant

% of TIC

MNav1 =mass of nitrate available in (i.e. returned to) the pre-D zone kg N · d−1

MNd =mass of denitrified nitrogen kg N · d−1

MNd1 =mass of nitrate denitrified in the pre-D reactor kg N · d−1

MNd3 =mass of nitrate denitrified in the post-D reactor kg N · d−1

MNdd =mass of nitrate denitrified in the final settler kg N · d−1

MNdp = denitrification due to consumption of slowlybiodegradable COD

kg N · d−1

MNds = denitrification due to consumption of easilybiodegradable COD

kg N · d−1

mNl = specific nitrogen discharge with the excess sludge mg N · mg−1 COD

MNl = nitrogen removal with produced excess sludge kg N · d−1

mNld = specific nitrogen release in digester mg N · mg−1 COD

MNld =mass of nitrogen released in digester kg N · d−1

mNle = specific nitrogen removal due to discharge with the stabilisedexcess sludge

mg N · mg−1 COD

MNle =mass of nitrogen removed with stabilised excess sludge kg N · d−1

MNlx =mass of nitrogen removed with the excess sludge corrected forthe loss of organic nitrogen with the effluent

kg N · d−1

MNte = nitrogen load in effluent kg N · d−1

MNti = nitrogen load in influent kg N · d−1

MOc = oxygen demand for COD oxidation (= MSo) kg O2 · d−1

MOeq = equivalent oxygen demand(recovered oxygen from denitrification)

kg O2 · d−1

MOn = oxygen demand for nitrification kg O2 · d−1

MOt = total oxygen demand kg O2 · d−1

MPchem =mass of phosphorus removed by chemical precipitation kg P · d−1

mPel = specific power production kWh · kg−1 COD

MPl = phosphorus removal with excess sludge production kg P · d−1

mPl = specific phosphorus discharge with the excess sludge mg P · mg−1 COD

MPl1 =mass of phosphorus removed with the primary excess sludge kg P · d−1

mPle = specific phosphorus removal due to discharge with thestabilised excess sludge

mg P · mg−1 COD

MPle =mass of phosphorus removed with stabilised excess sludge kg P · d−1

MPlex2 =mass of phosphorus removed with the secondaryexcess sludge, corrected for the loss of organic nitrogenwith the effluent

kg P · d−1

MPlx =mass of phosphorus removed with the excess sludge,corrected for loss of organic phosphorus in the effluent

kg P · d−1

Handbook of Biological Wastewater Treatmentxxxiv

MPte = phosphorus load in the effluent kg P · d−1

mq1 = specific primary excess sludge flow rate m3 · kg−1 COD

mq2 = specific secondary excess sludge flow rate m3 · kg−1 COD

mqth = specific thickened sludge production m3 · kg−1 COD

mSbu = fraction of total COD present as biodegradable CODin UASB effluent


mSd = fraction of influent COD that is digested mg COD · mg−1 COD

MSd =mass of COD digested in the system kg COD · d−1

MSda = COD mass digested in UASB and emitted to atmosphere kg COD · d−1

mSdu = fraction of influent COD digested in UASB mg COD · mg−1 COD

MSdu = COD mass digested in UASB kg COD · d−1

mSe = fraction of influent COD leaving the system withthe effluent (soluble COD only)


mSeu = fraction of influent COD ending up as non-settleableCOD in the UASB effluent


MSeu = non settleable COD load in UASB effluent kg COD · d−1

mSmb = fraction of influent COD metabolized mg COD · mg−1 COD

MSmb =metabolized sludge mass kg COD · d−1

mSo = fraction of influent COD that is oxidized mg COD · mg−1 COD

MSo =mass of COD oxidized in the system (= MOc) kg COD · d−1

mSod = fraction of influent COD oxidized in aerobic digester mg COD · mg−1 COD

MSseq =mass of COD sequestered by bio-P organisms kg COD · d−1

mSte = fraction of influent COD leaving the system withthe effluent (includes particulate COD)


MSte = COD load in the effluent kg COD · d−1

MSti = applied COD load kg COD · d−1

MSxv =mass of COD discharged from the system in theexcess sludge

kg COD · d−1

mSxv = fraction of influent COD discharged from the systemin the excess sludge


mSxv1 = fraction of influent COD leaving the system in theprimary excess sludge

kg COD · d−1

mSxv2 = fraction of influent COD discharged from the systemin the secondary excess sludge

kg COD · d−1

mSxve = fraction of influent COD leaving the system with stabilisedexcess sludge


MSxve =mass of COD discharged from the system inthe stabilised excess sludge

kg COD · d−1

mSxvu = influent COD fraction converted into anaerobicexcess sludge


Symbols, parameters and abbreviations xxxv

MSxvu = COD mass discharged as anaerobic excess sludgefrom the UASB

kg COD · d−1

mwmeoh =molecular weight metal hydroxide g · mol−1

mwmp =molecular weight metal phosphate g · mol−1

mwms =molecular weight metal salt g · mol−1

mXa = active sludge mass per unit mass daily applied COD mg VSS · d · mg−1 COD

MXa = total active sludge mass in system kg VSS

MXah = total active heterotrophic sludge mass in system kg VSS

MXan = total active nitrifier sludge mass in system kg VSS

MXap = total mass of active bio-P organisms in system kg VSS

mXau = active anaerobic sludge mass per unit mass daily applied COD mg VSS · d · mg−1 COD

MXau = total active anaerobic sludge mass in system kg VSS

mXbpu = non-degraded biodegradable sludge mass per unit mass dailyapplied COD


MXbpu = total mass of non-degraded biodegradablesludge mass in system

kg VSS

MXchem = total mass of chemical sludge in system kg TSS

mXe = endogenous sludge mass per unit mass daily applied COD mg VSS · mg−1 COD · d−1

MXe = total mass of endogenous sludge in system kg VSS

MXen = total mass of endogenous nitrifier sludge in system kg VSS

MXep = total mass of endogenous bio-P sludge in system kg VSS

mXeu = endogenous anaerobic sludge mass per unit massdaily applied COD


MXeu = total mass of endogenous anaerobic sludge kg VSS

mXi = inert sludge mass per unit mass daily applied COD mg VSS · d · mg−1 COD

MXi = total mass of inert sludge in system kg VSS

mXiu = non-biodegradable particulate anaerobic sludge massper unit mass daily applied COD


MXiu = total mass of non-biodegradable particulate anaerobicsludge in system

kg VSS

mXmu = inorganic anaerobic sludge mass per unit massdaily applied COD

mg ISS · d · mg−1 COD

MXmu = total mass of inorganic anaerobic sludge in system kg VSS

MXn = total nitrifier mass in system kg VSS

mXt = total sludge mass per unit mass daily applied COD mg TSS · d · mg−1 COD

MXt = total sludge mass in system kg TSS

MXtba = available sludge mass storage capacity in final settler kg TSS

MXtbr = required sludge mass storage capacity in final settler kg TSS

MXtd = total sludge mass in final settler kg TSS

mXtu = anaerobic sludge mass per unit mass daily applied COD mg TSS · mg−1 COD · d−1

Handbook of Biological Wastewater Treatmentxxxvi

MXtu = total mas of anaerobic sludge in system kg TSS

mXv = volatile sludge mass per unit mass daily applied COD mg VSS · mg−1 COD · d−1

MXv = total volatile sludge mass in system kg VSS

MXvh = total organic heterotrophic biomass in system kg VSS

mXvu = anaerobic organic sludge per unit mass daily applied COD mg VSS · mg−1 COD · d−1

MXvu = total anaerobic organic sludge mass in system kg VSS

n = economical lifetime years

n = number of gas boxes (–)

n = insurance costs % of TIC per year

N = number of UASB reactors (–)

N = number of aerobic digesters (–)

Nad = desired/required effluent ammonium concentration mg N · l−1

Nae = ammonium effluent concentration mg N · l−1

Nav1 = nitrate available in pre-D zone mg N · l−1 influent

Nav3 = nitrate available in post-D zone mg N · l−1 influent

Nc = nitrification capacity (= nitrified ammonium concentration) mg N · l−1 influent

Nc/Sbi = ratio between nitrification capacity and biodegradableinfluent COD

mg N/mg COD

(Nc/Sbi)l = limiting ratio between nitrification capacity and biodegradableinfluent COD for the Bardenpho process

mg N · mg−1 COD

(Nc/Sbi)o =maximum ratio between nitrification capacity andbiodegradable influent COD allowing full nitrogen removal

mg N · mg−1 COD

Nd = denitrified nitrogen concentration mg N · l−1 influent

Ndd = concentration of nitrate that will be denitrified in the returnsludge stream per passage through the final settler

mg N · l−1

Nddmax =maximum allowable production of nitrogen gas in the returnsludge flow during its passage through the final settler to theabstraction point

mg N · l−1

Ndp = denitrification due to consumption of slowlybiodegradable COD


Nds = denitrification due to consumption of easilybiodegradable COD


Nke = effluent Kjeldahl nitrogen concentration mg N · l−1

Nki = influent Kjeldahl nitrogen concentration mg N · l−1

Nl = nitrogen concentration removed with the excess sludge mg N · l−1 influent

Nld = nitrogen concentration released in digester mg N · l−1 influent

Nle = nitrogen concentration removed with the stabilisedexcess sludge


Nlh = nitrogen concentration removed with the heterotrophicexcess sludge


Symbols, parameters and abbreviations xxxvii

Nln = nitrogen concentration removed with the nitrifierexcess sludge


Nlx = nitrogen concentration discharged with excess sludge(corrected for loss of organic nitrogen in the effluent)


NN2eq = equilibrium dissolved nitrogen gas concentration at themaximum liquid depth of the final settler, assuming anatmosphere of 100% nitrogen

mg N · l−1

NN2in = dissolved nitrogen gas concentration in the incomingmixed liquor flow

mg N · l−1

Nn∞ = nitrate concentration when decay of active sludge is complete(aerobic digestion)

mg N · l−1

Nnd = nitrate production in the aerobic digester mg N · l−1

Nne = nitrate/nitrate effluent concentration mg N · l−1

Nni = initial nitrate concentration (aerobic digestion) mg N · l−1

Nni = influent nitrate/nitrite concentration mg N · l−1

Noe = organic nitrogen in effluent mg N · l−1

Noi = influent organic nitrogen concentration mg N · l−1

Nope = particulate organic nitrogen in effluent mg N · l−1

Nose = soluble organic nitrogen in effluent mg N · l−1

Np = nitrification potential (= maximum ammonium concentrationthat can be nitrified)


Nte = effluent total nitrogen concentration mg N · l−1

Nte,max =maximum nitrogen effluent concentration(all released nitrogen recycled to aeration tank)

mg N · l−1

Nte,min =minimum nitrogen effluent concentration(no recycle of released nitrogen to aeration tank)

mg N · l−1

Nti = influent Kjeldahl nitrogen concentration mg N · l−1

(Nti/Sti)l = limiting ratio between influent TKN and total influent COD forthe applicability of the Bardenpho process

mg N · mg−1 COD

(Nti/Sti)o =maximum ratio between influent TKN and total influent CODallowing full nitrogen removal

mg N · mg−1 COD

o = operational costs % of TIC per year

Oc = oxygen uptake rate (respiration) for COD oxidation mg O2 · l−1 · d−1

Oen = endogenous respiration rate mg O2 · l−1 · d−1

Oeq = oxygen recovery rate (equivalent oxygen uptake rate)due to denitrification

mg O2 · l−1 · d−1

Oex = exogenous respiration rate mg O2 · l−1 · d−1

Oex,sbp = exogenous respiration rate due to consumption of slowlybiodegradable (adsorbed) substrate

mg O2 · l−1 · d−1

Oex,sbs = exogenous respiration rate due to consumption of easilybiodegradable substrate

mg O2 · l−1 · d−1

Handbook of Biological Wastewater Treatmentxxxviii

On = oxygen uptake rate for nitrification mg O2 · l−1 · d−1

Ot = total oxygen uptake rate mg O2 · l−1 · d−1

OT4,5 = oxygen transfer efficiency at 4.5 m submergence %

OTa = actual oxygen transfer efficiency kg O2 · kWh−1 or %

Otd = total oxygen uptake rate (aerobic digester) mg O2 · l−1 · d−1

OTs = standard oxygen transfer efficiency kg O2 · kWh−1 or %

OUR = oxygen uptake rate mg O2 · l−1 · h−1

OURa = apparent OUR mg O2 · l−1 · h−1

OURabs = rate of change of oxygen concentration in reactordue to hydraulic effects

mg O2 · l−1 · h−1

OURen = endogenous respiration rate mg O2 · l−1 · h−1

OURh = rate of change of oxygen concentration in reactordue to adsorption of atmospheric oxygen

mg O2 · l−1 · h−1

OURm =maximum oxygen uptake rate due to nitrification mg O2 · l−1 · h−1

p = personnel costs % of TIC per year

p = atmospheric pressure bar

P = static point (–)

Paer = required aeration power kW

Paerm = installed aeration power kW

pch4 = partial methane pressure atm

Pchem = concentration of phosphorus to be chemically removed mg P · l−1 influent

pdis = discharge pressure bar or m liquid

Pdiss = dissipated power W · m−3

Pel = power production kW

Pel = electrical power consumption (pumps) kW

PEres = residual pollution load in wastewater after treatment US$ · PE−1

Ph = required heating power m3 gas or kg fuel · d−1

Pl = influent phosphorus concentration removedwith the excess sludge

mg P · l−1 influent

Pld = influent phosphorus concentration in digested sludge(i · e · released to liquid phase)


Ple = influent phosphorus concentration removed withthe stabilised excess sludge


Plx = phosphorus concentration discharged with excess sludge(corrected for loss of organic phosphorus with the effluent)


Pmin =minimum required energy required to keep sludge in suspension W · m−3

po2 = partial oxygen pressure atm

Pope = particulate organic phosphorus in effluent mg P · l−1

Pose = soluble organic phosphorus in effluent mg P · l−1

Ppe = phosphate concentration in effluent mg P · l−1

Symbols, parameters and abbreviations xxxix

ps = standard pressure bar

Ptd = desired/required total phosphorus concentration in the effluent mg P · l−1

Pte = effluent total phosphorus concentration mg P · l−1

Pte,max =maximum phosphorus effluent concentration(all released phosphorus recycled to aeration tank)

mg P · l−1

Pte,min =minimum phosphorus effluent concentration(no recycle of released phosphorus to aeration tank)

mg P · l−1

Pti = influent phosphorus concentration mg P · l−1

pw =water vapor pressure bar

Q = flow rate m3 · h−1 or m3 · s−1

q = excess sludge flow m3 · d−1

q1 = primary excess sludge flow m3 · d−1

q2 = secondary excess sludge flow m3 · d−1

Qair = air flow kg · h−1 or Nm3 · h−1

Qch4 =methane gas flow rate Nm3 · h−1

Qbg = biogas flow rate Nm3 · h−1

Qf =module feed flow (cross-flow membranes) m3 · h−1

Qi = influent flow rate m3 · d−1 or m3 · h−1

Qp = permeate flow rate m3 · h−1

Qpf = influent peak flow rate m3 · h−1

Qrec = recirculation flow (cross-flow MBR) m3 · h−1

qth = thickened excess sludge flow m3 · d−1

qw = excess sludge flow m3 · d−1

r = recirculation factor from pre-D zone to anaerobic zone (–)

R = gas constant kJ · mol−1 · K−1

ra = adsorption rate of slowly biodegradable material mg COD · l−1 · d−1

rd = decay rate mg VSS · l−1 · d−1

rd = denitrification rate mg N · l−1 · d−1

Rd = retention time in aerobic digester days

Rdi = retention time in anaerobic digester days

Rdmin = theoretical minimum total aerobic digestionretention time for N→ ∞

days

rdp = denitrification rate on slowly biodegradable COD mg N · l−1 · d−1

rds = denitrification rate on easily biodegradable COD mg N · l−1 · d−1

Rdtot =minimum total aerobic digestion retention time days

rg = growth rate mg VSS · l−1 · d−1

Rh = hydraulic retention time days

Rh1 = hydraulic retention time in pre-D reactor days

rhi = hydrolysis rate of stored slowly biodegradable material mg COD · l−1 · d−1

Handbook of Biological Wastewater Treatmentxl

Rhth = thickening time final settler (ATV) days

Rhu = hydraulic retention time UASB hr

Rmin =minimum retention time for complete utilisation of theSbs present in the influent in the pre-D reactor

days

rn = nitrification rate mg N · l−1 · d−1

RN = retention time in Nth aerobic digester days

Rrel = relative evaporation rate of water in the exposed sludge batch (–)

Rs = sludge age days

Rsa = true sludge age (including sludge mass present in final settler) days

rsbp = net production of slowly biodegradable material mg COD · l−1 · d−1

rsbs = net production of easily biodegradable material mg COD · l−1 · d−1

rsbs = feeding rate of easily biodegradable material to thepre-D reactor

mg COD · l−1 · d−1

Rsm =minimum sludge age required to achieve desiredeffluent ammonium concentration

days

Rsn =minimum sludge age required for nitrification days

rspa = net production of adsorbed biodegradable material mg COD · l−1 · d−1

Rsu = anaerobic sludge age days

ru = utilisation rate of organic material mg COD · l−1 · d−1

rus = utilisation rate of easily biodegradable influentorganic material

mg COD · l−1 · d−1

rv = decay rate of volatile solids mg VSS · l−1 · d−1

Rw =water evaporation rate mm · day−1

rxa = net production of active sludge mg VSS · l−1 · d−1

rxe = production rate of endogenous residue mg VSS · l−1 · d−1

s = sludge recycle factor (–)

Sbh = biodegradable COD consumed by normalheterotrophic biomass

mg COD · l−1 influent

Sbi = biodegradable influent COD concentration mg COD · l−1 influent

Sbp = biodegradable COD sequestered by bio-organisms mg COD · l−1 influent

Sbp = slowly biodegradable COD concentration (reactor) mg COD · l−1 influent

Sbs = easily biodegradable COD concentration (reactor) mg COD · l−1 influent

Sbsh = easily biodegradable COD consumed by normalheterotrophic biomass


S′bsi = influent concentration of easily biodegradable material aftercorrection for denitrification in the anaerobic zone


Sbsi = easily biodegradable influent COD concentration mg COD · l−1 influent

SbsN = residual concentration of the easily biodegradable materialin the effluent of the Nth reactor of a series

mg COD · l−1

Sbsp = easily biodegradable COD sequestered by bio-P organisms mg COD · l−1 influent

Symbols, parameters and abbreviations xli

sc = critical sludge recirculation factor (–)

sd = safety factor used to allow for locally increased dissolvednitrogen gas concentrations

(–)

Seu = soluble (non settleable) COD concentration in UASB effluent mg COD · l−1 influent

sfd = safety factor used in design final settler (–)

sfth = safety factor used in design sludge thickener (–)

Shab = COD discharge per capita g COD · inhab−1

smin =minimum value of sludge recirculation flow (MBR) (–)

Sni = non biodegradable influent COD concentration mg COD · l−1 influent

Snsi = non biodegradable soluble influent COD concentration mg COD · l−1 influent

Spa = concentration of absorbed slowly biodegradable material(reactor)


spf = return sludge ratio during peak flow (ATV) (–)

Spi = particulate influent COD concentration mg COD · l−1 influent

Ste = total effluent COD concentration mg COD · l−1

Sti = total influent COD concentration mg COD · l−1 influent

Stu = total UASB effluent COD concentration mg COD · l−1

SVFA =VFA concentration mg COD · l−1 influent

t = aerobic digestion time days

T = sewage temperature °C

t1 = time required for preparation of the sludge bed andapplication onto the bed of the sludge to be dried

days

t2 = time required for percolation days

t3 = time required for evaporation days

t4 = time required for removal of the dried sludge andcleaning of the bed for the next batch

days

tc = total drying cycle time days

TCC = total construction costs US$

tcomp = compression time (thickener) days

Tdig = temperature in the anaerobic digester °C

TIC = total investment costs US$

Tin = blower inlet temperature °C

Tmax =maximum reactor temperature °C

Tmin =minimum reactor temperature(often equal to design temperature)

°C

TOC = total operational costs US$

tp = duration of primary phase (denitrification) d

Ts = hydraulic loading rate m · h−1

Tsm =maximum allowable hydraulic loading rate m · h−1

Handbook of Biological Wastewater Treatmentxlii

Tspf = hydraulic loading rate during peak flow (ATV) m · h−1

Tvx = sludge volume loading rate l · m−2 · h−1

Tvxm =maximum sludge volume loading rate l · m−2 · h−1

u = downward liquid velocity in settler m · h−1

U = humidity %

Ue = final humidity %

Ui = initial humidity %

v0 =Vesilind constant m · d−1 or m · h−1

va = liquid velocity in UASB apertures m · h−1

Vaer = volume aerobic zone m3

Van = volume of anaerobic zone (bio-P removal) m3

Vc = volume of settler cone m3

vd = hydraulic retention time in final settler days

Vd = volume of final settler m3

Vd1 = volume of primary settler m3

Vda = aerobic digestion volume m3

vda = specific aerobic digestion volume m3 · d · kg−1 COD

Vdb = available volume for sludge buffering in the final settler m3

Vdi = anaerobic digester volume m3

Vhab = reactor volume required per capita m3 · inhab−1

vl = liquid upflow velocity in UASB reactor m · h−1

vo = liquid overflow velocity in UASB reactor m · h−1

Vr = volume of aeration tank m3

vr = biological reactor volume m3 · d · kg−1 COD

Vt = total volume m3

vth = specific thickener volume m3 · d · kg−1 COD

Vth = thickener volume m3

Vtp =molar gas volume at actual temperature and pressure liter · mol−1

Vu =UASB volume m3

vx = sludge volume ml · l−1

Vx1 = volume pre-D zone m3

Vx3 = volume post-D zone m3

Wa =width of single aperture in UASB reactor m

Wgb = outer width of gas box m

Wu =width of UASB reactor m

Xa = active sludge concentration in reactor kg VSS · m−3

Xa(N-1) = active sludge concentration in (N-1)th digester and its effluent(aerobic digestion)

kg VSS · m−3

Xad = digested active sludge concentration (aerobic digestion) kg VSS · m−3

Symbols, parameters and abbreviations xliii

Xae = active sludge concentration in digester and its effluent(aerobic digestion)

kg VSS · m−3

Xah,an = active heterotrophic sludge concentration inanaerobic zone

kg VSS · m−3

Xai = initial or incoming active sludge concentration(aerobic digestion)

kg VSS · m−3

XaN = active sludge concentration in N-th digester and its effluent(aerobic digestion)

kg VSS · m−3

Xan = active nitrifier concentration kg VSS · m−3

Xav = average concentration at which sludge will accumulatein the final settler

kg TSS · m−3

Xbpu = non degraded biodegradable solids concentration kg VSS · m−3

Xc = critical sludge concentration kg TSS · m−3

xch4 =mol fraction of dissolved methane gas in water mol · mol−1

Xd1 = primary sludge concentration kg TSS · m−3

Xe = concentration of endogenous residue in reactor kg VSS · m−3

Xee = endogenous sludge concentration formed in aerobic digester kg VSS · m−3

Xen = concentration of endogenous residue from nitrifiers kg VSS · m−3

Xf = average sludge concentration on settler bottom (ATV) kg TSS · m−3

Xi = inert organic sludge concentration in reactor kg VSS · m−3

Xl = limiting sludge concentration kg TSS · m−3

Xm =minimum sludge concentration kg TSS · m−3

Xmi = concentration of inorganic solids in influent mg ISS · l−1

Xmu = inorganic sludge concentration in reactor kg ISS · m−3

Xnae = inactive sludge concentration in digester (aerobic digestion) kg VSS · m−3

Xnai = initial or incoming inactive sludge concentration kg VSS · m−3

Xr = return sludge concentration kg TSS · m−3

Xrm =maximum return sludge concentration kg TSS · m−3

Xrmax =maximum allowed sludge concentration in membrane tank kg TSS · m−3

Xt = total sludge concentration in reactor kg TSS · m−3

Xt1 = sludge concentration in first reactor (step feed systems) kg TSS · m−3

Xt2 = sludge concentration in second reactor(step feed systems)

kg TSS · m−3

Xte = total stabilised sludge concentration kg TSS · m−3

Xte = effluent total solids concentration mg TSS · l−1

Xth = thickened excess sludge concentration kg TSS · m−3

Xthl = limiting thickening sludge concentration kg TSS · m−3

Xtpf = sludge concentration in the reactor during peak flow kg TSS · m−3

Xtu = average UASB sludge concentration in reactor kg TSS · m−3

Xtud = average UASB sludge concentration in digestion zone kg TSS · m−3

Handbook of Biological Wastewater Treatmentxliv

Xv = volatile sludge concentration in reactor kg VSS · m−3

Xv∞ = final volatile sludge concentration when decay of active sludgeis complete (aerobic digestion)

kg VSS · m−3

Xvd = digested organic sludge concentration kg VSS · m−3

Xve = stabilised organic sludge concentration kg VSS · m−3

Xvi = initial volatile sludge concentration (aerobic digestion) kg VSS · m−3

Xvu = organic anaerobic sludge concentration kg VSS · m−3

Xw =waste sludge concentration kg TSS · m−3

Yan = anaerobic yield mg VSS · mg−1 COD

Yao = yield of ammonia oxidisers mg VSS · mg−1 N

Yap = apparent yield mg VSS or TSS · mg−1 COD

Y or Yh = heterotrophic yield mg VSS · mg−1 COD

Yn = nitrifier yield mg VSS · mg−1 N

Yno = yield of nitrite oxidisers mg VSS · mg−1 N

α = inclination mm · m−1

α = ratio of the oxygen transfer rate in mixed liquor andin pure water

(–)

α = plate inclination or angle of base of V-notch º

β = ratio of the saturation concentration of DO in mixed liquorand in pure water

(–)

ΔAlkam = alkalinity change from ammonification mg CaCO3 · l−1 influent

ΔAlkd = alkalinity change from denitrification mg CaCO3 · l−1 influent

ΔAlkn = alkalinity change from nitrification mg CaCO3 · l−1 influent

ΔAlkt = total alkalinity change mg CaCO3 · l−1 influent

ΔDc1 = reduction in pre-D denitrification capacity due torecycle of oxygen to pre-D zone

mg N · l−1

ΔDc3 = reduction in post-D denitrification capacity due to influx ofoxygen in post-D zone

mg N · l−1

ΔL = height of water layer removed during drying period mm

ΔMXt =mass of sludge transferred from the reactor to the final settlerduring peak flow

kg TSS

ΔNa = variation of ammonium concentration mg N · l−1 influent

ΔNam = ammonified nitrogen concentration in theactivated sludge process


ΔNn = variation of nitrate concentration mg N · l−1 influent

Δp = differential pressure bar

Δpmod = differential pressure over a membrane module bar

ΔpTM = trans membrane pressure bar

ΔXt = change in reactor sludge concentration during peak flow g TSS · l−1

ηaer = efficiency of blower %

Symbols, parameters and abbreviations xlv

ηch4 =methane fraction in biogas %

ηCOD = COD removal efficiency %

ηd = efficiency factor to account for short circuiting betweeninlet- and outlet of final settler (ATV)

(–)

ηdn =maximum solids removal efficiency of inactive sludge fraction %

ηdp =maximum solids removal efficiency of active sludge fraction %

ηel = electrical efficiency of pump, biogas engine and gas motor %

ηm = ratio between net and gross membrane flux (–)

ηsb = sludge drying bed productivity kg TSS · m−2 · d−1

ηxv = fraction of solids converted in digester %

η1 = COD removal efficiency of primary settler %

ηdn = degree of solids conversion inert and endogenous sludge (–)

ηdp = degree of solids conversion active sludge (–)

ηx1 = solids removal efficiency of primary settler %

μ′m = (apparent) maximum specific nitrifier growth rate in systemswith non aerated zones

d−1

μ = specific growth rate of nitrifiers d−1

μm =maximum specific nitrifier growth rate d−1

νT/T,ref = sweet water viscosity at process temperature or T= 15°C cP

ρ = density kg · m−3

Φ =membrane permeability litre · m−2 · h−1 · bar−1

ΦT/T,ref =membrane permeability at process temperature/at T= 15°C litre · m−2 · h−1 · bar−1

θ = temperature dependency coefficient (Arrhenius) (–)

ω = contraction coefficient (–)

Handbook of Biological Wastewater Treatmentxlvi

Documents

Handbook of - ENPAB · Handbook of Biological Wastewater Treatment Design and Optimisation of Activated Sludge Systems Second Edition A.C. van Haandel and J.G.M. van der Lubbe